Minnesota Power now estimates that some 5.5 million gallons of water, siphoned off the top of a disposal site for coal ash, spilled through a cracked pipe outside its coal plant.

When the Duluth-based utility first reported the spill earlier this week, it had estimated that 1 million gallons of the tainted water had bubbled up from an underground pipe. The pipe sends the liquid back into the Boswell Energy Center in Cohasset, Minn., for re-use.

A “significant portion” of the water saturated the ground around the spill, the company now says. At least some of the water reached Blackwater Creek, flowing on to Blackwater Lake, a dammed section of the Mississippi River, according to Minnesota Power and the Minnesota Pollution Control Agency.

“The updated spill volume does not change the spill mitigation and response activities underway at the site and has been reported to regulators,” the utility’s statement read.

It is not clear how concentrated the pollution in the spilled water is. It was sucked up from on top of a pond where the plant had previously deposited fly ash, or fine particles that are carried by flue gases, between 1980 and 2015.

“The MPCA remains focused on evaluating concentrations and extent of potential pollutants released and the impacts to soils, Blackwater Creek and Lake, aquatic life and wild rice beds,” the agency wrote.

Testing is underway for what contaminants might have spread from the spill, and MPCA said Friday that it had hired its own contractor for sampling and monitoring at the site.

Both MPCA and the utility said that sulfate, a mineral salt, has been found in levels above state limits in place to protect wild rice, but below levels of concern for drinking water. In addition to the sulfate, tests of the creek have also found higher levels of boron, an element that occurs in coal ash but that is not necessarily harmful to people who consume it.

Initial testing has not found mercury, arsenic and selenium, all common components in coal ash, from the area of the creek where contamination is highest, according to Minnesota Power’s statement.

MPCA and the Minnesota Department of Health have been evaluating downstream drinking water users, but almost all use wells. The next downstream community to draw its drinking water directly from the Mississippi River is St. Cloud, according to an MDH statement.

Cleanup crews on the site had already installed booms in the water and an earthen berm. Now, Minnesota Power said it plans to excavate tainted soil as part of its mitigation efforts. The area has been surveyed for cultural resources in consultation with the Leech Lake Band of Ojibwe, which has reservation lands to the west of the spill site.